Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$39.84	6.131%	$42.2826	$42.28	$42.30	$42.30
Purchase #2	$141.84	11.768%	$158.5317	$158.53	$158.55	$158.50
Purchase #3	$207.65	7.829%	$223.9069	$223.91	$223.90	$223.90
Purchase #4	$186.87	9.115%	$203.9032	$203.90	$203.90	$203.90
Purchase #5	$81.97	10.429%	$90.5187	$90.52	$90.50	$90.50
Purchase #6	$85.96	13.495%	$97.5603	$97.56	$97.55	$97.60
Purchase #7	$160.86	12.260%	$180.5814	$180.58	$180.60	$180.60
7 purchase totals =	$904.99		$997.2848	$997.28	$997.30	$997.30